298 CALKINS. 



EXPLANATION OF PLATE XVII. 



Fig. r. A section through the testis, showing position of the latter in relation 

 to the dissepiment. There is no distinct membrane about the testis as there is in 

 the case of the ovary. The nuclei at the extremity of the testis are arranged in 

 groups of varying size. Each group consists of spermatogonia, and each group 

 is one multinucleate cell. 



Fig. 2. A multinucleate cell in the testis, showing the general distribution of 

 the nuclei throughout the cell. Optical section. 



Fig. 3. Multinucleate cell in a seminal vesicle, showing a peripheral arrange- 

 ment of the nuclei before the cytoplasmic cleavages have taken place. Optical 

 section. 



Fig. 4. A multinucleate cell in the seminal vesicles, showing the beginning of 

 cytoplasmic cleavage very similar to the cleavage of a centrolecithal egg. The 

 interior cytoplasm is finely granular. At the extremity of the nucleus is a large 

 mass of archoplasm which is characteristic of the resting stage. 



Fig. 5. An eccentric spermatosphere, showing distortion of the blastophore, 

 increase of spermatocytes of the first order, anaphase of karyokinesis, reconstruc- 

 tion of archoplasm at spindle poles, and beginning of cytoplasmic cleavage with 

 traces of interzonal fibres in some cells. 



Fig. 6. A spermatosphere in a late stage, showing elongation of spermatids 

 with beginning of tail formation at the free end of the cell. The archoplasm is at 

 the distal extremity of the homogeneous and compact nucleus. 



Fig. 7. A spermatogonium in the testis from a multinucleate cell, showing the 

 nuclear plate with 32 apparently single chromosomes. 



Fig. 8. A spermatogonium from the testis in full karyokinesis, showing 24 of 

 the 32 chromosomes and the archoplasm reduced by the picric acid to a mere dot 

 at the poles. 



